Process for conversion of a deasphalted oil

ABSTRACT

The invention relates to a process for conversion of a heavy feedstock that has a boiling point of more than 340° C. for at least 80% by weight of the feedstock, a Conradson carbon content of at least 5% by weight, an asphaltene content of at least 1% by weight, a sulfur content of at least 0.5% by weight, and a metal content of at least 20 ppm, process in which: Said feedstock is subjected to deasphalting, and a deasphalted oil that contains less than 1% by weight of asphaltenes is obtained At least a portion of said oil, and preferably all of it, is subjected directly to hydroconversion in the presence of a supported or dispersed catalyst, and the effluent that is obtained is distilled to separate a residue At least part if not all of said residue is recycled with the feedstock to deasphalting.

The invention relates to a process for hydroconversion of heavy petroleum feedstocks, for example of the residue type such as atmospheric residue (AR) or vacuum residue (VR), to produce gasolines, gas oils, and vacuum gas oils.

A conventional concatenation of the VR/AR conversion process consists in a stage of deasphalting with solvent (SDA) followed by a hydroconversion stage of the DAO (deasphalted oil), then distillation so as to transform it into products of high added value (gasoline, middle distillates, VGO: vacuum gas oil, vacuum residue).

The drawback of this type of scheme is that it is virtually impossible to complete a total conversion of the DAO into converted products, whereby the residue is evacuated outside of the unit. To enhance the conversion, it was recommended to recycle by hydroconversion the hydroconversion residue that was separated by distillation. This approach is limited because of the very refractory nature of the DAO in the total hydroconversion, especially since these are heavy DAOs, i.e., extracts with solvents ranging from C4 (butane) to C6 (hexane). It therefore is not possible to achieve a total conversion of the DAO in a hydroconversion unit that operates in liquid recycling mode.

A process has now been sought for the production of gasoline and gas oil with good yields and good qualities by a simple and economical process, in particular with recycling of the DAO to the point of extinction, which eliminates the drawbacks cited above.

The invention relates to a process in which the DAO is converted completely to the point of its total extinction by recycling the unconverted residue at the very input of the deasphalting unit. The asphaltenes that are produced in the hydroconversion stage will then be eliminated in the SDA unit and will be found in the asphalt phase, so that the recycled DAO, which is virtually free of asphaltene, will penetrate the hydroconversion unit, mixed with the “straight-run” (SR) DAO and will crack in the hydroconversion unit with, however, a conversion rate that is slightly lower than the SR DAO.

Thus, with a conversion per pass of slightly less recycled DAO than that of the SR DAO, a total conversion of the DAO into products of high added value is achieved at the end of several passages. It appears that the asphalt yield increases only slightly relative to the scheme without recycling because of the accumulation of small quantities of asphaltenes that are formed in the hydroconversion stage.

More specifically, the invention relates to a process for conversion of a heavy feedstock that has a boiling point of more than 340° C. for at least 80% by weight of the feedstock, a Conradson carbon content of at least 5% by weight, an asphaltene content of at least 1% by weight, a sulfur content of at least 0.5% by weight, and a metal content of at least 20 ppm, process in which:

-   -   Said feedstock is subjected to deasphalting, and a deasphalted         oil that contains less than 1% by weight of asphaltenes is         obtained     -   At least a portion, and preferably all, of said oil is subjected         directly to hydroconversion in the presence of a supported or         dispersed catalyst, and the effluent that is obtained is         distilled to separate a residue     -   All of said residue is recycled with the feedstock to         deasphalting.

The invention is explained with reference to FIG. 1.

The feedstock is generally of the residue type. It generally has a Conradson carbon content of at least 5% by weight and generally at least 10% by weight, an asphaltene content (IP143 Standard/with C7) of at least 1%, often at least 2%, and very often at least 5% by weight, and can even equal or exceed 24% by weight. Their sulfur content is generally at least 0.5%, often at least 1%, and very often at least 2%, and even up to 4% or even 10% by weight. The quantities of metals that they contain are generally at least 20 ppm by weight, often at least 50 ppm, and typically at least 100 ppm or at least 200 ppm by weight.

Such feedstocks are partially topped, for example stripped, crude oils, atmospheric residues, vacuum residues, atmospheric or vacuum residues that are obtained from the distillation of crude oils (SR) or obtained from a process for primary conversion of an atmospheric or vacuum residue (such as visbreaking, hydroconversion . . . ) or else atmospheric or vacuum residues that are obtained from light to medium or heavy conventional crude oils (for example, Middle East, Ural, West African, . . . ) or extra-heavy crude oils that have, for example, an API of less than 15 (crude oils of Venzuela, Canada, . . . ).

It is also possible to include carbons or cokes that are advantageously introduced in suspension.

The feedstocks are generally characterized by a boiling point of more than 340° C. for at least 80% by weight of the feedstock, and preferably for at least 90% by weight of the feedstock. The process applies particularly to the heavy feedstocks that have a boiling point of more than 500° C., and even 540° C., for at least 80% by weight of the feedstock, or, preferably, for at least 90% of the feedstock. They generally have (fresh feedstocks) a viscosity of less than 100,000 cSt at 100° C., and even less than 40,000 cST, and preferably less than 20,000 cST at 100° C. They should generally be converted to produce finished products such as gas oil, gasoline and GPL, of lower boiling point.

BRIEF DESCRIPTION OF DRAWINGS

The attached drawing is a block flowsheet of a preferred comprehensive embodiment of the convention.

DETAILED DESCRIPTION OF THE FLOWSHEET

The feedstock that comes in via the pipe 1 is sent into the deasphalting unit 2. The residue that is obtained from the distillation, which will be described later, is added via the pipe 11 to this feedstock.

The deasphalting stage using a solvent is carried out under conditions that are well known to one skilled in the art.

It is possible to use, for example, the processes such as Solvahl, Rose, . . . .

The deasphalting is usually carried out at a temperature of 60 to 250° C. with at least one hydrocarbon-containing solvent that has 3 to 7 carbon atoms and is optionally diluted with at least one additive. The usable solvents and the additives are extensively described. These are, as indicated above, for example, C4 to C6, and more particularly C5 or C6. It is also possible and advantageous to carry out the recovery of the solvent according to the opticritical process, i.e., by using a solvent under non-supercritical conditions. This process makes it possible in particular to improve significantly the overall economy of the process. This deasphalting can be done in a mixer-decanter or in an extraction column.

Within the scope of this invention, the technique that uses at least one extraction column and advantageously a single one is preferred. Advantageously, as in the Solvahl process with a single extraction column, the starting solvent/feedstock ratios of SDA are low, between 4/1 and 6/1. In addition to an excellent extraction of metals and asphaltenes, this makes it possible to have only very small quantities of solvent in the DAO. The deasphalting unit produces a DAO (deasphalted oil) that is virtually free of asphaltenes and an asphalt (pipe 13) that concentrates the majority of the impurities of the residue and that is drawn off. The management of the solvent that is known to one skilled in the art has not been shown. The DAO yield can vary by less than 50% by weight to more than 90% by weight.

The DAO has an asphaltene content that is reduced to less than 1% by weight in general (C7 measurement), preferably to less than 0.5%, most often to less than 0.05% (Solvahl process, for example), and even more preferably to less than 0.3% by weight, measured in C5 insoluble products, and to less than 0.05% by weight, measured in C7 insoluble products (Solvahl process, for example).

At least one portion of DAO, and preferably all of it, is sent into a hydroconversion unit 3.

The hydroconversion stage therefore makes possible a partial conversion of the residue into products that are lighter than the feedstock (gas, gasoline, middle distillates, vacuum distillates VGO) by leaving a certain quantity of residue unconverted; it can be used according to various processes, such as the commercial processes below:

-   -   The fixed-bed hydroconversion processes, preferably followed by         a visbreaking unit (Hyvahl, preferably followed by a visbreaking         unit, Unibon . . . ) that operate with moderate conversions per         pass that are typically of less than 50% by weight but at least         20% by weight or else at least 30% by weight     -   The moving-bed hydroconversion processes with semi-continuous         addition of supported catalyst that operate with moderate         conversions per pass that are typically of less than 50% by         weight but at least 20% by weight or else at least 30% by         weight.     -   The boiling-bed processes that operate advantageously with a         semi-continuous addition of catalyst (H oil, LC fining . . . )         that operate with high conversions per pass, generally of at         least 60% by weight. This type of process is preferred.     -   The slurry hydroconversion processes (HDHPLUS, EST . . . ) that         operate with generally high conversions per pass of at least 50%         by weight or at least 60% and preferably at least 80% by weight         or their combinations.

The fixed-bed or boiling-bed processes are preferred.

The conversion is defined as being the ratio (% by weight of residue in the feedstock−% of residue in the product)/% of residue in the feedstock, for the same feedstock-product fraction point; typically, this fraction point is between 450 and 550° C., and often about 500° C.; in this definition, the residue being the boiling fraction starting from this fraction point (such as 500° C.+, for example).

For the boiling-bed processes, generally, at least one conventional hydroconversion catalyst is used. This catalyst is generally a catalyst that comprises a substrate, generally amorphous, which is preferably an alumina, and at least one metal from Group VIII (for example, nickel and/or cobalt), most often combined with at least one metal from group VIB (for example, molybdenum). It is possible, for example, to use a catalyst that comprises 0.5 to 10% by weight of nickel and preferably 1 to 5% by weight of nickel (expressed in terms of nickel oxide NiO) and 1 to 30% by weight of molybdenum, preferably 5 to 20% by weight of molybdenum (expressed in terms of molybdenum oxide MoO₃) on a substrate, for example, an alumina substrate. This catalyst is most often in the extrudate or ball form. The mechanical resistance of the substrates is high for the boiling-bed operation.

The procedure is usually performed in this stage under an absolute pressure of 5 to 35 MPa and most often from 10 to 25 MPa at a temperature of about 300 to about 500° C. and often from about 350 to 450° C. The VVH of the liquid and the partial hydrogen pressure are selected based on the characteristics of the feedstock to be treated and the desired conversion. Most often, the VVH of the liquid is from about 0.1 to about 5 h⁻¹, and preferably from about 0.15 to about 2 h⁻¹. The waste catalyst is partially replaced by fresh catalyst according to the known methods of one skilled in the art.

In this stage, a catalyst is advantageously used, ensuring both the demetallization and the desulfurization, under conditions that make it possible to obtain a liquid feedstock with a reduced content of metals, Conradson carbon and sulfur and that make it possible to obtain a high conversion.

This type of boiling-bed process associated with the SDA is therefore particularly advantageous for treating the DAOs that often contain more than 30 ppm of metals.

In the fixed-bed processes, generally, at least one conventional hydroconversion catalyst fixed bed is used. The procedure is performed usually under an absolute pressure of 5 to 35 MPa and most often from 10 to 20 MPa at a temperature from about 300 to 500° C. and often from about 350 to 450° C. The VVH and the partial pressure of hydrogen are selected based on the characteristics of the feedstock that is to be treated and the desired conversion. Most often, the VVH is in a range that goes from about 0.1 to about 5 h⁻¹ and preferably about 0.15 to about 2. The quantity of hydrogen that is mixed with the feedstock is usually from about 100 to about 500 normal cubic meters (Nm³) per cubic meter (m³) of liquid feedstock and most often from about 500 to about 3000 Nm³/m³.

The ideal catalyst should have a strong hydrogenating power so as to carry out a deep refining and to obtain a significant reduction in sulfur, Conradson carbon and asphaltene content. It is possible, for example, to use one of the catalysts described by the applicant in the patents EP-B-113297 and EP-B-113284.

Regarding the processes that run on slurry, i.e., in the presence of a circulated, dispersed, catalytic phase, they generally operate under a total pressure of 1-50 MPa, preferably 2-30 MPa, with a partial hydrogen pressure that varies from 1 to 50 MPa, preferably 2 to 30 MPa, with a temperature of 300 to 600° C., preferably 400 to 470° C., whereby the contact is carried out for a certain time that is necessary to the conversion of the residue, ranging from 5 nm to 20 h, preferably between 1 and 10 h.

The catalysts are well known to one skilled in the art and are obtained from the thermal decomposition of catalytic precursors (for example, molybdenum naphthenate, etc . . . ).

The effluent that is obtained at the end of the hydroconversion stage (exiting via the pipe 4) is distilled in the atmospheric column 5, and gasoline (pipe 6), gas oil (pipe 7) and an atmospheric residue (pipe 8 of FIG. 1) are obtained. Advantageously, the atmospheric residue is vacuum-distilled (column 9), and VGO (vacuum gas oil via the pipe 10) and a vacuum residue (pipe 11) are obtained.

In the atmospheric distillation zone 5, the conditions are generally selected such that the fraction point for the residue is from about 300 to about 400° C. and preferably from about 340 to about 380° C. The distillates [gasoline fraction (pipe 8), and gas oil fraction (pipe 9)] that are thus obtained are usually sent to the corresponding fuel pools. Before being sent there, the gas oil that is produced by the process according to the invention is hydrotreated in a subsequent unit 12, under operating conditions and with catalysts that are usually used and known to one skilled in the art so as to bring the sulfur content to market specifications, which is less than 10 ppm of sulfur, and to improve the cetane index. Before being sent to the gasoline pool, the gasoline fraction is generally treated by reforming (not shown in the Figure).

Preferably, the atmospheric residue (pipe 8) is sent to vacuum distillation.

In the vacuum distillation zone 9, the conditions are generally selected so that the fraction point for the residue is from about 450 to 600° C. and most often from about 500 to 550° C. The vacuum distillate fraction(s) (VGO) obtained exit(s) via the pipe(s) 10 and the vacuum residue via the pipe 11.

The VGO is advantageously sent at least in part into a catalytic cracking unit 13.

According to the invention, the atmospheric residue or preferably the vacuum residue is recycled at least in part, and preferably entirely, into the feedstock that goes into asphalting.

Thus, the total conversion is at least 20% or at least 30% by weight, and in the case of the boiling beds, at least 60%, and even at least 80%, and in the case of the slurry, most often, at least 80%.

EXAMPLE

The feedstock is an extra-heavy vacuum residue of Canadian origin. The table below records the properties of this residue as well as those of the DAO that is obtained by pentane deasphalting of this residue (Solvahl process): TABLE 1 VR DAO Density 1.07 0.994 Viscosity at 100° C. cSt 30640 192.2 Conradson Carbon % by Weight 21.9 8.5 C7 Asphaltene % by Weight 14.9 Nickel ppm 137 20 Vanadium ppm 337 35 Nitrogen ppm 6000 3249 Sulfur % by Weight 5.4 4.05

This DAO is treated, on the one hand, in the conventional scheme by boiling-bed hydroconversion followed by an atmospheric distillation and a vacuum distillation without recycling of the vacuum residue, and, on the other hand, in the scheme according to the invention with recycling of the entire vacuum residue to the deasphalting. The hydroconversion is performed under the same conditions as the 2 cases: 10 MPa of hydrogen and 440° C. in the presence of an NiMo/alumina catalyst. The yields are indicated in % by weight relative to a base 100 of initial VR (Table 2). TABLE 2 % by Weight vs. VR Feed SDA + HCK SDA + HCK Without Recycling Recycle Conventional Scheme Scheme of the Invention H₂S + NH₃ 3.0 3.0 Gas: 3.6 4.3 Gasoline: 9.7 11.5 Diesel: 18.5 22.3 VGO: 18.8 22.7 VR: 13.0 0.0 DAO SDA Purge 35.0 38.0 Total 101.5 101.8 H₂ Consumption 1.5 1.8

With the conventional scheme, advantageous yields of converted products are obtained, but there remains, however, 13% of vacuum residue that has a very low value. The asphalt that is produced represents 35% by weight of the starting vacuum residue.

With the scheme according to the invention with recycling of the unconverted residue in the deasphalting unit, the quantity of asphalt slightly increases to 38% versus 35% in the conventional scheme, but in contrast, the yields of light products increase significantly, in particular the diesel fraction rises from 18.5% by weight in the conventional scheme to 22.3% of yield in the diagram according to the invention. The VGO fraction rises from 18.8 to 22.7% by weight.

This example demonstrates that it is possible, contrary to the preconceived idea that one skilled in the art had, of recycling the entire deasphalted hydroconversion vacuum residue by increasing the gas oil and gasoline yields while maintaining suitable product qualities and without reducing the service life of the catalyst, and without large quantities of asphalt being produced.

It was demonstrated here that the refractory compounds were eliminated in the deasphalting.

The invention therefore makes it possible to obtain gasoline and gas oil fractions with very good yields with good qualities of products with an economic process.

Furthermore, with the process according to the invention, it could be noted that it was possible to produce a very good feedstock for the catalytic cracking (FCC) that is the VGO that does not contain refractory asphaltenes with catalytic cracking. Thus, the VGO can be sent directly to the FCC and without pre-treatment.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

The entire disclosures of all applications, patents and publications, cited herein and of corresponding French application No. 06/08.803, filed Oct. 6, 2006 are incorporated by reference herein.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. 

1. A process for conversion of a heavy feedstock that has a boiling point of more than 340° C. for at least 80% by weight of the feedstock, a Conradson carbon content of at least 5% by weight, an asphaltene content of at least 1% by weight, a sulfur content of at least 0.5% by weight, and a metal content of at least 20 ppm, said process comprising: subjecting said feedstock to deasphalting, to obtain a deasphalted oil that contains less than 1% by weight of asphaltenes subjecting at least a portion of said deasphalted oil directly to hydroconversion in the presence of a supported or dispersed catalyst, and distilling the resultant effluent to separate a residue, and recycling at least part of said residue with the feedstock to said deasphalting.
 2. A process according to claim 1, wherein all of the deasphalted oil is subjected to hydroconversion.
 3. A process according to claim 1, wherein the feedstock has a boiling point of more than 540° C. for at least 80% by weight of the feedstock and a viscosity that is lower than 100,000 cSt at 100° C.
 4. A process according to claim 1, wherein the hydroconversion stage is conducted in a boiling bed with a conversion per pass of at least 60% by weight.
 5. A process according to claim 1, wherein the hydroconversion stage is conducted in a fixed bed with a conversion of greater than or equal to 20% by weight and less than 50% by weight.
 6. A process according to claim 1, wherein the hydroconversion stage is conducted in a moving bed with a conversion of greater than or equal to 20% by weight and less than 50% by weight.
 7. A process according to claim 1, wherein the hydroconversion stage is conducted as a slurry with a conversion of at least 50% by weight.
 8. A process according to claim 7, wherein the hydroconversion stage is conducted at a temperature of 400-470° C. and with a conversion of at least 80% by weight.
 9. A process according to claim 1, wherein said feedstock is directly subjected to deasphalting.
 10. A process according to claim 1, wherein all of the residue is fed to the deasphalting.
 11. A process according to claim 2, wherein all of the residue is fed to the deasphalting.
 12. A process according to claim 11, wherein said feedstock is directly subjected to deasphalting. 